Process chambers used in the semiconductor, physics research, surface and materials science industries are frequently required to accurately maintain predetermined pressures to successfully provide the proper environment that is best suited for the particular process.
Closed loop servo driven valves for maintaining predetermined pressures in process chambers are known in the prior art. Such valves are typically driven by a motor, such as a stepper motor.
Prior art closed loop, servo motor driven valves maintain a desired pressure with logic including a pressure transducer to provide a controller with an analog signal representing the pressure within the process chamber. The controller compares this signal to a predetermined set point pre-programmed into the controller, or communicated to it via a computer or an external analog input representing the desired pressure. The controller then typically sends a digital signal to the motor component of the valve to open or close the valve accordingly until the pump or compressor of the process chamber adjusts its output to produce a signal from the pressure transducer that is equal to the set point in the controller.
Inertia of the motor components may slow the closed loop adjustments. Additionally, oscillation may occur with the use of motor driven valves when the system searches for the set point because of the limited resolution of the digital output versus the analog input.
Because of the critical requirements of semiconductor processes and the like, secondary pneumatic valves or battery backups for the motor driven valves are typically required to quickly close and isolate the process in the event of a power failure. The use of backup equipment increases system cost and requires additional components that may generate particles which contaminate processes, reduce the conductance in the system, and increase maintenance operations.
As can be seen by the discussion of the prior art, and unsolved need exists for a pneumatic closed loop servo system for a variable conductance pressure regulating valve that overcomes the drawbacks of the prior art and provides both system pressure control and positive shutoff functions.